The biology of the macrophage surface as it relates to phenomena of spreading and of particle recognition needs to be further developed. This information is relevant to the role of macrophages in inflammation, in the immune response and in delayed hypersensitivity reactions. The proposed work will: a) Examine different inducers of in vitro macrophage spreading (immune complexes, proteolytic enzymes, thiols) as to their mechanism(s) of action. Characterize and examine the biological properties of a spreading inhibitor present in serum and in peritoneal exudate supernatants. Compare induced macrophage spreading in vitro with the spreading of in vivo activated macrophages. Investigate the effect of lymphokines on induced macrophage spreading. b) Characterize the mechanisms involved in the phagocytic recognition of damaged cells by macrophages.